1. Technical Field
The invention relates to a heating system for vehicles. More particularly, the invention relates to a heating system for a motor vehicle that includes an additional heater element.
2. Discussion
A heating system of the generic type is known from DE 44 36 943 C2, this system having, on the one hand, a heater connected to the coolant circuit of the internal combustion engine and, on the other hand, an additional heater independent of the internal combustion engine. The additional heater heats the heating water, the temperature of which is below a temperature set by the thermostat. With the additional heater switched off, the heated engine coolant flows via the heat exchanger, for which purpose the switching element has an inlet chamber, which is connected to the cooling circuit of the internal combustion engine, and a discharge chamber, which is connected both to the heat exchanger and to the additional heater, and also has a nonreturn valve which is arranged between the inlet and the discharge chamber and the shut-off direction of which is towards the engine. The nonreturn valve has an actuating element which raises the valve element of the nonreturn valve from its valve seat above a predetermined temperature in the inlet chamber.
This manner of operating a heating system has the disadvantage that when the engine is running, especially in the high engine-speed range, the pressure in the coolant circuit is so high that the heating water heated by the additional heater cannot enter the coolant circuit. The pressure of the heating water has to be increased with the aid of a more powerful pump to allow the heating water to enter the cooling circuit. More powerful pumps have the disadvantage that they are expensive and large. Thus, more space must be provided for the installation of a larger pump, and this is not available, particularly in vehicle construction.